Somethimes there is only few entries but somethimes several dozens all in the same time.This applies not all my pools but some of them in randow way.
Iteresting is the last one with SIGKILL.

I found this in fpm source code https://github.com/php/php-src/blob/master/sapi/fpm/fpm/fpm.h#L29
but i don't have any idea what is responsible for that kind of behaviour.
I've tried to minimize pm.max_requests=1000 but without any improvement.